Hope you can find Bullseye.....
But if you can't find it there are similar powders that you might not like as well (I love BE myself) buy if you can find something to hold off until more powders become available, even if just a pound or two.
Like Accurate #2, Alliant Red Dot, W231 are pretty close.
Hodgdon Titegroup is a fast target powder but many think it burns a little hot. It's also really touchy on charge weight. I have a couple of pounds but haven't used it enough to say much.
Accurate 5 and Unique are a lower on the ladder of burning speed but they would be a good near substitute.
Hit the manuals and the internet and I'll bet you can come up with more close substitutes.
BTW Trail Boss would work for target lead bullets because it was specifically designed for 'cowboy' shooting.